{"html":"<!DOCTYPE html>\n<html>\n\n<head>\n    <meta charset=\"UTF-8\">\n    <style>\n        \n        div{\n            position: relative/* 确保伪元素可以相对于div定位 */\n        }\n\n        div::after{\n            content:\"\";/*内容*/\n            display: block;/*伪元素能够按照块级元素进行显示*/\n            width: 20px;\n            height: 20px;\n            background-color: rgb(255,0,0);\n        }\n    \n    </style>\n</head>\n\n<body>\n    <div></div>\n    <script type=\"text/javascript\">\n        // 填写JavaScript\n    </script>\n</body>\n\n</html>","css":"","js":""}